Mars Global Surveyor's first look at Mars is showing
scientists a world devoid of an active core and anything more
than the relic of an ancient magnetic field.

"Mars no longer has a global magnetic field generated by an
internal energy source, like Earth and the other planets," said
Dr. Jack Connerney, co-investigator of the magnetometer/electron
spectrometer team, at an Oct. 2 Mars Global Surveyor press
briefing at NASA's Jet Propulsion Laboratory. "It appears that
the crust of Mars is strewn with multiple magnetic anomalies,
which may represent the solidification of magma as it was coming
up through the crust and cooling very early in Mars' evolution,
but this is only the memory of a magnetic field."

Mars Global Surveyor went into orbit around Mars on Sept. 11
after a 10-month journey to the planet, and detected the presence
of a weak magnetic field within a week of its arrival. Evidence
of this faint magnetic field confirmed long-standing theories
that the red planet had, at one time in its history, a liquid
core able to support a dynamo. Scientists believe this core
probably froze and solidified early in the planet's evolution.

The magnetometer data, acquired during one of the
spacecraft's highly elliptical orbits around Mars during the week
of Sept. 15-18, indicates that the planet's magnetic field is
not globally generated in the planet's core, but is localized in
particular areas of the crust, said Dr. Daniel Winterhalter,
magnetometer experiment representative at JPL. Scientists plan
to correlate these strong magnetic anomalies with topographical
data obtained by Global Surveyor's camera and laser altimeter.
That information may lead to the identification of particular
topographic features in the crust.

"The identification of these magnetic anomalies and their
correlation with surface features may enable us to trace the
history of the planet's interior, just as we are able to trace
the history of Earth's interior using the magnetic anomalies that
have been imprinted on the ocean floors," Winterhalter said.

Mars' very localized field also creates a new paradigm for
the way in which it interacts with the solar wind, one that is
not found with other planets. While Earth, Jupiter and other
planets have large magnetospheres, and planets like Venus have
strong ionospheres, Mars' small, localized magnetic fields are
likely to produce a much more complicated interaction process as
these fields move with the planet's rotation.

These observations and many more came just as the spacecraft
finished the walk-in phase of aerobraking and was about to begin
the main phase, which will last three months. All six of the
spacecraft's science instruments had been turned on midway
through the elliptical walk-in phase for calibration and
engineering adjustments. Since its capture, the spacecraft's
orbit has been reduced from 45 hours to 40 hours, 20 minutes.
Through January 1998, the aerobraking and navigation teams will
gradually circularize Surveyor's orbit into the final two-hour,
378-kilometer (234-mile) mapping orbit.

"The spacecraft and science instruments are operating
magnificently," reported Dr. Arden Albee, of the California
Institute of Technology, Pasadena, CA, who is the Mars Global
Surveyor project scientist. "The initial science data we've
obtained from the walk-in phase of aerobraking are remarkable in
their clarity, and the combined measurements from all of the
instruments over the next two years are going to provide us with
a fascinating new global view of the planet."

Mars Global Surveyor carries six science instruments -- a
camera, laser altimeter, magnetometer/electron reflectometer,
thermal emission spectrometer and ultra-stable oscillator -- that
will paint a global portrait of Mars, gathering data on the
planet's atmosphere, surface and interior. The mission will
enable scientists to determine Mars' current state and some of
the major turning points in its evolution. Among a myriad of
science objectives, Global Surveyor will study Mars' climate and
its resources, and attempt to determine if life ever existed on
the planet.

During the past three weeks, the spacecraft has been
aerobraking through the upper atmosphere of Mars each time it
passes closest to the surface. Aerobraking operations are
continuing to proceed smoothly. The spacecraft has completed 12
revolutions around Mars, including nine aerobraking passes
through the upper Martian atmosphere, said Dr. Richard Zurek, an
investigator at JPL who is leader of the Mars Global Surveyor
atmospheric advisory team. Each of these atmospheric passes
takes place at the start and low point of the orbit, known as the
periapsis, as Global Surveyor orbits at current altitudes of
about 110 kilometers (70 miles).

So far, the upper atmospheric density has varied according
to daytime and nighttime measurements by as much as 70 percent,
said Dr. Gerald Keating, on the atmospheric advisory team from
George Washington University, Washington, DC, and densities are
five times higher than they were when the Mars Pathfinder
spacecraft entered the upper atmosphere on July 4. Density
profiles are being acquired on a daily basis and used to help
guide the aerobraking team's work to shrink and circularize the
spacecraft's orbit. Although the thickness of the Martian
atmosphere continues to run slightly higher than predicted, no
major changes to the aerobraking strategy are being considered
because the spacecraft was designed to tolerate up to a 70
percent increase in atmospheric thickness.

The first orbital images of the Martian surface in more than
20 years are showing geologic features that would dwarf some of
the most spectacular features known to Earth. Initial science
data show a canyon far deeper than Arizona's 1-mile-deep Grand
Canyon and mountains standing much taller than Nepal's Mt.
Everest. Vast expanses of smooth crustal flatlands in the
northern hemisphere hint at a geologically younger portion of
Mars, while new measurements of the planet's southern polar cap
indicate drastically frigid temperatures of about minus 129
degrees Celsius (minus 200 degrees Fahrenheit).

Mars Global Surveyor's camera revealed two regions of
interest to geologists: a view of a highland valley network
called Nirgal Vallis and an image of Labyrinthus Noctis, an area
west of the Valles Marineris near the crest of a large updoming
in the Martian crust. The images were presented by Dr. Michael
Malin, of Malin Space Science Systems Inc., San Diego, CA, who is
the principal investigator of the Mars Global Surveyor camera.

Nirgal Vallis is about 15 kilometers (9 miles) across by
about 45 kilometers (27 miles) in length, with many small sand
dunes and different aged craters in the vicinity, Malin said. The
valley is located at 28.5 degrees south latitude, 41.6 degrees
west longitude. Of interest to scientists are the processes that
helped shape this canyon.

"The origin of this and many other canyons on Mars has been
debated ever since the Mariner 9 mission," Malin said. "There are
two leading theories: the first suggests that water flowing over
the surface accumulated, as it does on Earth, then formed a
drainage basin that allowed the water to flow further down into a
larger channel. The alternative explanation was that ground
water processes dissolved part of the subterranean materials on
Mars, causing collapse and progressive deterioration of this
particular region."

Labyrinthus Noctis, the second image presented Oct. 2, is
near the crest of a large updoming of the Martian crust that is
probably thousand of kilometers in diameter, and near very large,
2,000-meter-deep (6,500-foot) canyons bounded by faults. Debris
shed from the steep slopes has moved down into the region after
the canyons opened. Small dunes are seen in the lower portion of
this area, beneath the high cliffs.

Global Surveyor's camera has acquired about a dozen high
resolution images of Mars to date, which are being used to fine-
tune the instrument in preparation for the start of mapping
operations in March 1998. These first images were not the highest
resolution expected during mapping because the spacecraft is not
yet in the proper mapping orbit and the correct sunlight
conditions have not yet been reached, Malin said. As the
spacecraft moves into its Sun-synchronous orbit, in which it will
cross the Martian equator at 2 p.m. local Mars time during each
revolution, the Sun will be at a standard angle above the horizon
in each image.

The spacecraft's thermal emission spectrometer recorded sub-
freezing temperatures at the southern polar cap, said principal
investigator Dr. Philip Christensen of Arizona State University,
Tempe. The instrument, which takes infrared measurements on the
surface, also recorded temperature highs of about -7 C (20 F) at
the warmest parts of the planet and a very clear, dust-free
atmosphere.

The laser altimeter, which fires 10 laser pulses a second at
the surface, is also performing well, reported Dr. David Smith,
principal investigator of the instrument and based at the NASA
Goddard Space Flight Center, Greenbelt, MD. This experiment will
measure the height of Martian surface features and provide
elevation maps that will be precise to within 30 meters (98 feet)
of surface features. From the 12,000 measurements already taken,
Smith reported a notable inaccuracy in the location of some
Martian features as shown on current maps based on Viking data.
Global Surveyor will provide a much more accurate global map
which will be used to guide future missions to the surface.

Mars Global Surveyor is the first in a sustained program of
Mars exploration, known as the Mars Surveyor Program. The
mission is managed by the Jet Propulsion Laboratory for NASA's
Office of Space Science, Washington, DC. JPL's industrial partner
is Lockheed Martin Astronautics, Denver, CO, which developed and
operates the spacecraft. JPL is a division of the California
Institute of Technology, Pasadena, CA.